This paper focuses on the nexus between state infrastructural power and legitimacy. A comparative case study of nationalism in mid-20th century Mexico and Argentina provides the basis for theorising the impact of state infrastructural power on transformations of official national ideology. Both countries experienced a transition from liberal to popular nationalism. Yet, the extent to which popular nationalism became a regular product of state organisations varied between the two cases, depending on the timing of state development. The temporal congruence between the expansion of state infrastructural power and ideological change, as exemplified by Mexico under Cýrdenas, facilitated the full institutionalisation of the new official ideology, whereas a disjuncture between state development and ideological change, as exemplified by Argentina under Perýn, inhibited such a comprehensive transformation of nationalism.